Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	$ 1,666	$ 2,148
Gross Unrealized Losses, Less than 12 Months	74	31
Estimated Fair Value, 12 Months or Longer	64	272
Gross Unrealized Losses, 12 Months or Longer	3	14
Estimated Fair Value, Total	1,730	2,420
Gross Unrealized Losses, Total	77	45
Corporate and other bonds
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	609	914
Gross Unrealized Losses, Less than 12 Months	21	21
Estimated Fair Value, 12 Months or Longer	12	186
Gross Unrealized Losses, 12 Months or Longer	1	11
Estimated Fair Value, Total	621	1,100
Gross Unrealized Losses, Total	22	32
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	33	34
Gross Unrealized Losses, Less than 12 Months	0	0
Estimated Fair Value, 12 Months or Longer	0	0
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	33	34
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	71	249
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	11	30
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	82	279
Gross Unrealized Losses, Total	1	1
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	533	381
Gross Unrealized Losses, Less than 12 Months	40	3
Estimated Fair Value, 12 Months or Longer	28	20
Gross Unrealized Losses, 12 Months or Longer	2	2
Estimated Fair Value, Total	561	401
Gross Unrealized Losses, Total	42	5
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	344	449
Gross Unrealized Losses, Less than 12 Months	9	3
Estimated Fair Value, 12 Months or Longer	13	33
Gross Unrealized Losses, 12 Months or Longer	0	1
Estimated Fair Value, Total	357	482
Gross Unrealized Losses, Total	9	4
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	948	1,079
Gross Unrealized Losses, Less than 12 Months	50	7
Estimated Fair Value, 12 Months or Longer	52	83
Gross Unrealized Losses, 12 Months or Longer	2	3
Estimated Fair Value, Total	1,000	1,162
Gross Unrealized Losses, Total	52	10
U.S. Treasury and obligations of government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	63	62
Gross Unrealized Losses, Less than 12 Months	3	2
Estimated Fair Value, 12 Months or Longer	0	2
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	63	64
Gross Unrealized Losses, Total	3	2
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value, Less than 12 months	13	59
Gross Unrealized Losses, Less than 12 Months	0	1
Estimated Fair Value, 12 Months or Longer	0	1
Gross Unrealized Losses, 12 Months or Longer	0	0
Estimated Fair Value, Total	13	60
Gross Unrealized Losses, Total	$ 0	$ 1